Use throwRecoverableException instead of raw throw for stored exceptions

Replace `throw kj::mv(*exception)` with `kj::throwRecoverableException(kj::mv(*exception))` in the async worker thread exception handler.

A raw throw creates a kj::Exception with the calling binary's typeinfo. On macOS with -fvisibility=hidden, this typeinfo is not coalesced with libkj.dylib's copy by the dynamic linker, so getCaughtExceptionAsKj()'s catch (kj::Exception& e) fails and falls through to catch (...), producing "unknown non-KJ exception of type: kj::Exception" errors.

throwRecoverableException() routes the throw through libkj, wrapping it in ExceptionImpl with consistent typeinfo. This matches the pattern KJ uses internally in kj/async-inl.h when re-throwing stored exceptions from promises.

Author: alfonsoromanz

include/mp/type-context.h

@@ -189,7 +189,7 @@ auto PassField(Priority<1>, TypeList<>, ServerContext& server_context, const Fn&
             }
         })) {
             MP_LOG(loop, Log::Error) << "IPC server request #" << req << " uncaught exception (" << kj::str(*exception).cStr() << ")";
-            throw kj::mv(*exception);
+            kj::throwRecoverableException(kj::mv(*exception));
         }
         return call_context;
         // End of scope: if KJ_DEFER was reached, it runs here